Hyphenated techniques Flashcards
Electrospray Ionization (ESI)?
High voltage creates charged droplets → ions for MS.
Ideal for proteins/DNA; “gentle” ionization.
APCI (Atmospheric Pressure Chemical Ionization)?
Heated nebulizer + chemical reactions ionize molecules.
Best for small, neutral molecules (e.g., drugs).
APPI (Atmospheric Pressure Photo-Ionization)?
UV light ionizes non-polar compounds (e.g., steroids).
Used for hydrocarbons, lipids.
What distinguishes Traditional LC from HPLC?
HPLC uses smaller particles (<40 μm), high pressure, and offers better efficiency, narrower peaks, and faster separation compared to Traditional LC (>150 μm particles, low pressure).
What are two major issues when coupling LC with MS?
Incompatible buffers (MS requires volatile buffers) and flow rate mismatch (1 mL/min liquid ≈ 500 mL/min gas in MS vacuum).
How does LC-MS improve upon HPLC?
LC-MS combines separation with identification/quantification, offering higher sensitivity, specificity, and faster analysis.
Which ionization method is suitable for large, thermally labile biomolecules?
Electrospray Ionization (ESI) or MALDI.
What type of compounds is APCI used for?
Small, non-polar, thermally stable molecules (e.g., steroids, lipids).
Which matrix is used for proteins in MALDI?
What flow rates can APCI handle?
500–2000 μL/min.
Key Mnemonics
ESI for “Electrospray” → Envelops large biomolecules.
APCI → Atmospheric Pressure for Chemicals (small molecules).
MALDI → Matrix Assists Large DNA/proteins.
How is GC-MS used in environmental analysis?
A: Detecting pesticides, volatile organic compounds, and pollutants.
Q: What is the advantage of a quadrupole analyzer?
A: Compact, cost-effective, fast scan rates, but limited resolution.
